Temporary wet strength additives

ABSTRACT

Temporary wet strength additives, more particularly, temporary wet strength additives comprising a polymer backbone, wherein the polymer backbone has an internal homo-crosslinking monomeric unit, a co-crosslinking monomeric unit and a cationic monomeric unit, wherein the homo-crosslinking monomeric unit is derived from a monomer having the following structure: 
                         
and X is —O—,—NH—, or —NCH 3 —; and R 2  is a substituted or unsubstituted aliphatic groups; and Y 3  is —H, —CH 3 , or a halogen, fibrous structures including such temporary wet strength additives, sanitary tissue products containing such fibrous structures and processes for making such fibrous structures and/or such sanitary tissue product are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/958,016 filed Oct. 4, 2004, now U.S. Pat. No. 7,258,763, which is acontinuation-in-part application of U.S. application Ser. No. 10/687,381filed Oct. 16, 2003, now U.S. Pat. No. 7,125,469.

FIELD OF THE INVENTION

The present invention relates to temporary wet strength additives, moreparticularly, to temporary wet strength additives comprising a polymerbackbone, wherein the polymer backbone comprises a co-crosslinkingmonomeric unit, preferably a reversible co-crosslinking monomeric unit,especially in the presence of water, a homo-crosslinking monomeric unitand a cationic monomeric unit, fibrous structures comprising suchtemporary wet strength additives, sanitary tissue products comprisingsuch fibrous structures and processes for making such fibrous structuresand/or such sanitary tissue product. Such fibrous structures andsanitary tissue products exhibit high initial wet tensile strength andimproved flushability and/or reduced-clogging properties.

BACKGROUND OF THE INVENTION

Wet strength is a desirable attribute of many disposable sanitary tissueproducts that come into contact with aqueous fluids during use, such asnapkins, paper towels, household tissues (for example, facial and/ortoilet tissue), disposable hospital wear, etc. In particular, it isoften desirable that such sanitary tissue products have sufficient wetstrength to enable their use in a moistened or wet condition. However,sanitary tissue products containing temporary wet strength additives,such as toilet tissue, must be capable of decaying in a relatively shortamount of time so that they do not clog sewage systems and/or septictanks.

Accordingly, the use of temporary wet strength additives in sanitarytissue products requires balancing sufficient wet strength of thesanitary tissue product during use with the ability of the sanitarytissue product to decay rapidly and effectively in an aqueousenvironment after use. In particular, there is a need for sanitarytissue products that maintain a greater percentage of their dry strengthwhen they are first wetted, while, on further and/or subsequent exposureto water and/or other aqueous solutions, show a substantial decay,preferably rapidly and effectively, of their initial wet strength suchthat the used sanitary tissue product effectively flushes thusmitigating clogging of sewage systems and/or septic tanks.

SUMMARY OF THE INVENTION

The present invention fulfills the need described above by providing afibrous structure comprising a temporary wet strength additive such thatthe fibrous structure and/or sanitary tissue product made therefromexhibits sufficient flushability and/or decaying properties, especiallyin the presence of water and/or other aqueous solutions.

In one aspect of the present invention, a temporary wet strengthadditive comprising a polymer backbone comprising a co-crosslinkingmonomeric unit, a homo-crosslinking monomeric unit and a cationicmonomeric unit is provided.

In another aspect of the present invention, a temporary wet strengthadditive exhibiting a Tg of less than about 100° C. is provided. Tg isdetermined using differential scanning calorimetry. In one embodiment, atemporary wet strength additive exhibiting a glass transitiontemperature, “Tg”, of from about 45° C. to about 100° C. is provided. Inanother embodiment, a temporary wet strength additive exhibiting a Tg offrom about 50° C. to about 95° C. is provided. In still anotherembodiment, a temporary wet strength additive exhibiting a Tg of fromabout 55° C. to about 90° C. is provided. In even still anotherembodiment, a temporary wet strength additive exhibiting a Tg of fromabout 60° C. to about 85° C. is provided.

In yet another aspect of the present invention, a fibrous structurecomprising a temporary wet strength additive according to the presentinvention is provided.

In even yet another aspect of the present invention, a sanitary tissueproduct comprising a fibrous structure of the present invention isprovided.

In still another aspect of the present invention, a process for making afibrous structure of the present invention is provided.

In still another aspect of the present invention, a process for making asanitary tissue product of the present invention is provided.

In even another aspect of the present invention, a method for making atemporary wet strength additive in accordance with the present inventionis provided.

Accordingly, the present invention provides novel temporary wet strengthadditives, fibrous structures and/or sanitary tissue products comprisingsuch temporary wet strength additives, processes for making such fibrousstructures and/or sanitary tissue products, processes for making suchtemporary wet strength additives and fibrous structures and/or sanitarytissue products comprising such temporary wet strength additives thatexhibit improved flushability and/or reduced-clogging as compared tofibrous structures and/or sanitary tissue products that contain priorart temporary wet strength additives.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

“Fibrous structure” as used herein means a substrate formed fromnon-woven fibers. The fibrous structure of the present invention may bemade by any suitable process, such as wet-laid, air-laid, sponbondprocesses. The fibrous structure may be in the form of one or more pliessuitable for incorporation into a sanitary tissue product and/or may bein the form of non-woven garments, such as surgical garments includingsurgical shoe covers, and/or non-woven paper products such as surgicaltowels and wipes.

“Fiber” as used herein means an elongate particulate having an apparentlength greatly exceeding its apparent width, i.e. a length to diameterratio of at least about 10. More specifically, as used herein, “fiber”refers to papermaking fibers. The present invention contemplates the useof a variety of papermaking fibers, such as, for example, natural fibersor synthetic fibers, or any other suitable fibers, and any combinationthereof. Papermaking fibers useful in the present invention includecellulosic fibers commonly known as wood pulp fibers. Applicable woodpulps include chemical pulps, such as Kraft, sulfite, and sulfate pulps,as well as mechanical pulps including, for example, groundwood,thermomechanical pulp and chemically modified thermomechanical pulp.Chemical pulps, however, may be preferred since they impart a superiortactile sense of softness to tissue sheets made therefrom. Pulps derivedfrom both deciduous trees (hereinafter, also referred to as “hardwood”)and coniferous trees (hereinafter, also referred to as “softwood”) maybe utilized. The hardwood and softwood fibers can be blended, oralternatively, can be deposited in layers to provide a stratified web.U.S. Pat. No. 4,300,981 and U.S. Pat. No. 3,994,771 are incorporatedherein by reference for the purpose of disclosing layering of hardwoodand softwood fibers. Also applicable to the present invention are fibersderived from recycled paper, which may contain any or all of the abovecategories as well as other non-fibrous materials such as fillers andadhesives used to facilitate the original papermaking. In addition tothe above, fibers and/or filaments made from polymers, specificallyhydroxyl polymers may be used in the present invention. Nonlimitingexamples of suitable hydroxyl polymers include polyvinyl alcohol,starch, starch derivatives, chitosan, chitosan derivatives, cellulosederivatives, gums, arabinans, galactans and mixtures thereof.

“Sanitary tissue product” as used herein means a soft, low density (i.e.<about 0.15 g/cm³) web useful as a wiping implement for post-urinary andpost-bowel movement cleaning (toilet tissue), for otorhinolaryngolicaldischarges (facial tissue), and multi-functional absorbent and cleaninguses (absorbent towels).

“Ply” or “Plies” as used herein means an individual fibrous structureoptionally to be disposed in a substantially contiguous, face-to-facerelationship with other plies, forming a multiple ply fibrous structure.It is also contemplated that a single fibrous structure can effectivelyform two “plies” or multiple “plies”, for example, by being folded onitself.

“Basis Weight” as used herein is the weight per unit area of a samplereported in lbs/3000 ft² or g/m². Basis weight is measured by preparingone or more samples of a certain area (m²) and weighing the sample(s) ofa fibrous structure according to the present invention and/or a paperproduct comprising such fibrous structure on a top loading balance witha minimum resolution of 0.01 g. The balance is protected from air draftsand other disturbances using a draft shield. Weights are recorded whenthe readings on the balance become constant. The average weight (g) iscalculated and the average area of the samples (m²). The basis weight(g/m²) is calculated by dividing the average weight (g) by the averagearea of the samples (m²).

“Weight average molecular weight” as used herein means the weightaverage molecular weight as determined using gel permeationchromatography according to the protocol found in Colloids and SurfacesA. Physico Chemical & Engineering Aspects, Vol. 162, 2000, pg. 107-121.Unless otherwise specified, all molecular weight values herein refer tothe weight average molecular weight.

“Co-crosslinking” as used herein means a reaction between the temporarywet strength additive of the present invention and a fiber whereby thetemporary wet strength additive is covalently bonded to the fiber.

“Homo-crosslinking” as used herein means a reaction between thetemporary wet strength additive of the present invention and anothertemporary wet strength additive of the present invention or aconventional temporary wet strength additive wherein the temporary wetstrength additives are covalently bonded to one another.

“Electrophilic moiety” as used herein means a moiety which is capable ofaccepting electrons from a nucleophilic moiety in order to form acovalent bond between the nucleophilic moiety and itself.

“Nucleophilic moiety” as used herein means a moiety which is capable offorming a covalent bond with an electrophilic moiety under chemicaland/or physical conditions conventionally experienced during fibrousstructure-making and/or sanitary tissue product-making processes and/orduring storage and/or use of fibrous structures and/or sanitary tissueproducts comprising the temporary wet strength additives of the presentinvention.

“Unstable, covalent bond” as used herein means a covalent bond that isreversible in the presence of water and/or an aqueous fluid. Anonlimiting example of an unstable, covalent bond is a hemi-acetal bondformed by reacting a hydroxyl moiety with an aldehyde moiety.

“Stable, covalent bond” as used herein means a covalent bond that is notreversible in the presence of water and/or an aqueous fluid. Anonlimiting example of a stable, covalent bond is an amidol bond formedby reacting an amide moiety with an aldehyde moiety.

“Non-nucleophilic moiety” as used herein means a moiety which is notcapable of reacting with an electrophilic moiety to form a covalent bondunder chemical and/or physical conditions conventionally experiencedduring fibrous structure-making and/or sanitary tissue product-makingprocesses and/or during storage and/or use of fibrous structures and/orsanitary tissue products comprising the temporary wet strength additivesof the present invention.

“Decay” as used herein means the percent loss of wet tensile strength.

Fibrous Structures/Sanitary Tissue Products

The fibrous structure (web) of the present invention may be incorporatedinto a single-ply or multi-ply sanitary tissue product.

The fibrous structure may be foreshortened, such as via creping and/ormicrocontraction and/or rush transferring, or non-forshortened, such asnot creping; creped from a cylindrical dryer with a creping doctorblade, removed from a cylindrical dryer without the use of a crepingdoctor blade, or made without a cylindrical dryer.

The fibrous structures of the present invention are useful in paper,especially sanitary tissue paper products including, but not limited to:conventionally felt-pressed tissue paper; pattern densified tissuepaper; and high-bulk, uncompacted tissue paper. The tissue paper may beof a homogenous or multilayered construction; and tissue paper productsmade therefrom may be of a single-ply or multi-ply construction. Thetissue paper preferably has a basis weight of between about 10 g/m² andabout 120 g/m², and density of about 0.60 g/cc or less. Preferably, thebasis weight will be below about 35 g/m²; and the density will be about0.30 g/cc or less. Most preferably, the density will be between about0.04 g/cc and about 0.20 g/cc.

The fibrous structure may be selected from the group consisting of:through-air-dried fibrous structures, differential density fibrousstructures, wet laid fibrous structures, air laid fibrous structures,conventional fibrous structures and mixtures thereof.

The fibrous structure may be made with a fibrous furnish that produces asingle layer embryonic fibrous web or a fibrous furnish that produces amulti-layer embryonic fibrous web.

The fibrous structures of the present invention and/or paper productscomprising such fibrous structures may have a total dry tensile ofgreater than about 59 g/cm (150 g/in) and/or from about 78 g/cm (200g/in) to about 394 g/cm (1000 g/in) and/or from about 98 g/cm (250 g/in)to about 335 g/cm (850 g/in).

The fibrous structures of the present invention and/or paper productscomprising such fibrous structures may have a total wet tensile strengthof greater than about 9 g/cm (25 g/in) and/or from about 11 g/cm (30g/in) to about 78 g/cm (200 g/in) and/or from about 59 g/cm (150 g/in)to about 197 g/cm (500 g/in).

A nonlimiting suitable process for making a fibrous structure of thepresent invention comprises the steps of providing a furnish comprisinga plurality of cellulosic fibers and a wet strength agent; forming afibrous structure from the furnish and heating/drying the fibrousstructure to a temperature of at least about 40° C. and a moisturecontent of less than about 5%.

Fibrous Structure Additives

Any fibrous structure/sanitary tissue product additives, including wetstrength additives, known to those skilled in the art may beincorporated into the fibrous structures and/or sanitary tissue productsof the present invention so long as the fibrous structures/sanitarytissue products exhibit improved wet strength properties, as describedherein, as compared to conventional fibrous structures/sanitary tissueproducts.

The temporary wet strength additives of the present invention can beused in any type of fibrous structure and/or sanitary tissue productconstruction. These include: pattern densified tissue paper such as, butnot limited to, that disclosed in U.S. Pat. No. 3,301,746, Sanford andSisson, issued Jan. 31, 1987, U.S. Pat. No. 3,974,025, Ayres, issuedAug. 10, 1976, U.S. Pat. No. 4,191,609, Trokhan, issued Mar. 4, 1980,U.S. Pat. No. 3,821,068, Shaw, issued Jun. 28, 1974, U.S. Pat. No.3,573,164, Friedberg et al., issued Mar. 30, 1971, and U.S. Pat. No.3,994,771, Morgan et al., issued Nov. 30, 1976, all incorporated byreference herein; uncompacted, nonpattern-densified tissue paper suchas, but not limited to, that disclosed in U.S. Pat. No. 3,812,000,Salvucci et al., issued May 21, 1974 and U.S. Pat. No. 4,208,459, Beckeret al., issued Jun. 17, 1980, both incorporated by reference herein; andconventional tissue paper well known in the art, typically made bypressing a wet web at elevated temperatures to dewater and dry said web.

The temporary wet strength additives of the present invention are usefulfor a wide variety of paper and paper products. As used herein, theterms “paper” and “paper products” include sheet-like masses and moldedproducts containing fibrous cellulosic materials which may be derivedfrom natural sources, such as wood pulp fibers, as well as other fibrousmaterial characterized by having hydroxyl groups attached to the polymerbackbone. These include glass fibers and synthetic fibers modified withhydroxyl groups. Cellulosic fibers are preferred. In addition, thepresent invention encompasses papers made from combinations ofcellulosic fibers, or other fibers having hydroxyl-substituted polymerchains, and other fibrous or nonfibrous materials known to the art. Thepaper products of the present invention preferably contain at leastabout 70%, more preferably at least about 85%, by weight (dry sheetproduct basis), cellulosic fibers. Suitable nonfibrous additions aredescribed in Young, “Fiber Preparation and Approach Flow” Pulp and PaperChemistry and Chemical Technology, Vol. 2, pp. 881-882, which isincorporated herein by reference.

The temporary wet strength additives of the present invention areparticularly useful for nonwoven tissue paper products containingcellulosic fibers such as toilet paper, facial tissue, and paper towels.These products will typically have basis weights of between about 8 g/m²and about 65 g/m², and densities of between about 0.03 g/cm³ and about0.60 g/cm³. They can be made according to any of the techniques known tothe art.

In forming fibrous structures and/or sanitary tissue products, thetemporary wet strength additives of the present invention are preferablyadded as dilute aqueous solutions at any point in the papermakingprocess where temporary wet strength additives are customarily added.

The temporary wet strength additives typically are readily absorbed bythe cellulose fibers in an aqueous environment at pH values within therange of about 3.5 to about 8.0. The wet strength additives can developwet strength in fibrous structures and/or sanitary tissue productswithin this pH range.

Typically, the temporary wet strength additive of the present inventiondevelops its wet strength in fibrous structures and/or sanitary tissueproducts both at room temperature and at temperatures at which paper isconventionally dried or through-air dried (190° F.-250° F./87° C.-121°C.).

While Applicants do not wish to be bound by theory, it is believed thatwet strength in the fibrous structures and/or sanitary tissue productsof the present invention is generated by the formation of hemiacetalbonds, which form when the temporary wet strength additive of thepresent invention bonds to the cellulose (co-crosslinking); and byhemiacetal bonds, which form when the temporary wet strength additivethat is attached to one cellulose fiber bonds to a hydroxyl moiety ofanother temporary wet strength additive that is attached to anotherfiber (homo-crosslinking). In order to lose wet strength, these same twobonds must break. By controlling the relative number of these bonds, thewet tensile strength and the rate of tensile decay of the celluloseproduct upon wetting can be controlled.

In forming fibrous structures and/or sanitary tissue products of thepresent invention, the temporary wet strength additives of the presentinvention can be added as dilute aqueous solutions at any point in thepapermaking process where temporary wet strength additives arecustomarily added. Such nonfibrous additions are described in Young,“Fiber Preparation and Approach Flow” Pulp and Paper Chemistry andChemical Technology, Vol. 2, pp 881-882, which is incorporated byreference.

The temporary wet strength additive of the present invention can beapplied to the fibrous slurry and/or in-line in a fibrous structuremaking machine (i.e., papermaking machine) and/or in the furnish, and/orto the embryonic fibrous web and/or fibrous structure and/or sanitarytissue product of the present invention as it is being made on apapermaking machine or thereafter: either while it is wet (i.e., priorto final drying) or dry (i.e., after final drying). Application methodsfor applying the temporary wet strength additive may include spraying onto the embryonic fibrous web directly or contacting the foraminous wireand/or fabric and/or belt which contacts the web with the temporary wetstrength additive, such as by spraying and/or dipping and/or slotextruding and/or brushing on.

A substantial amount of initial wet strength is imparted to the fibrousstructures and/or sanitary tissue products of the present invention whenfrom about 0.005% to about 2% of the temporary wet strength additive byweight of the fiber is added. Typically, best results, i.e., around 50%of tensile decay at 5 minutes and around 80% at 30 minutes, are achievedwhen about 0.1% to about 0.3% of the temporary wet strength additive byweight of the fiber is added, and when from 30 mole percent to about 85mole percent of the homo-crosslinking monomeric unit is present in thetemporary wet strength additive. When lower levels of thishomo-crosslinking monomeric unit are added, there is an insufficientamount of wet tensile decay over time. When greater than 85% of thenon-nucleophilic monomeric unit is present, the fibrous structuresand/or sanitary tissue products of the present invention do not exhibitgood initial wet strength.

A nonlimiting example of a suitable wet strength additive for use in thefibrous structures and/or sanitary tissue products of the presentinvention includes temporary wet strength additives described herein.

Temporary Wet Strength Additives

Nonlimiting examples of suitable temporary wet strength additives foruse in the fibrous structures of the present invention generally haveweight average molecular weights of from about 20,000 to about 400,000and/or from about 50,000 to about 400,000 and/or from about 70,000 toabout 400,000 and/or from about 70,000 to about 300,000 and/or fromabout 100,000 to about 200,000.

In forming fibrous structures and/or sanitary tissue products of thepresent invention, wet strength additives, if present, can be added asdilute aqueous solutions at any point in the papermaking process wherewet strength additives are customarily added. Such nonfibrous additionsare described in Young, “Fiber Preparation and Approach Flow” Pulp andPaper Chemistry and Chemical Technology, Vol. 2, pp 881-882, which isincorporated by reference.

In one embodiment, the fibrous structures of the present inventioncomprise from about 0.005% to about 5% and/or from about 0.1% to about2% and/or from about 0.1% to about 1% by weight of the fiber.

The temporary wet strength additives of the present invention impart wettensile strength properties and wet tensile decay properties to thefibrous structures and/or sanitary tissue products of the presentinvention.

It has been found that temporary wet strength additives with high weightaverage molecular weights (i.e. those in excess of 300,000) may decayunacceptably slow for consumer purposes. They may not achieve a wettensile decay rate of better than 35-45% after 5 minutes and/or betterthan 50-65% after 30 minutes.

Further, it has been found that temporary wet strength additives withextremely low weight average molecular weights (i.e. those less than70,000) may have very low wet strength and are may not be optimal astemporary wet strength additives for fibrous structures and/or sanitarytissue products.

The temporary wet strength additives in accordance with the presentinvention have the formula:

wherein: A (the moiety present on the co-crosslinking monomeric unit) isindependently an electrophilic moiety, nonlimiting examples of whichinclude the following:

Z (the moiety present on the homo-crosslinking monomeric unit) isindependently a nucleophilic moiety capable of forming an unstablecovalent bond with the electrophilic moiety, nonlimiting examples ofwhich include the following:

and X is independently —O—, —NH—, or —NCH₃—; and R₁ and R₂ areindependently substituted or unsubstituted aliphatic groups; Y₁, Y₂, andY₃ are independently —H, —CH₃, or a halogen; Q is a cationic moiety; andW is a non-nucleophilic moiety or a nucleophilic moiety that does notform a stable covalent bond with the electrophilic moiety. Nonlimitingexamples of moieties for W include water-soluble nitrogen heterocyclicmoieties and/or water-soluble carboxylic acid moieties.

The mole percent of a ranges from about 1% to about 47%, preferably fromabout 5% to about 30%, the mole percent of b ranges from about 0% toabout 60%, preferably from about 0% to about 45%, the mole percent of cranges from about 10% to about 90%, preferably from about 30% to about80%, and d ranges from about 1% to about 40%, preferably from about 2%to about 20%, more preferably from about 5% to about 12%.

Unless otherwise expressly specified, values for a, b, c, and d shall bemole percentage values based upon the average number of monomeric unitsin the polymer backbone of the temporary wet strength additive of thepresent invention.

The monomeric units of the polymer backbone of the temporary wetstrength additive of the present invention are randomly distributedthroughout the polymer in ratios corresponding to the mole percentageranges described herein.

Each class of monomeric units may include a single monomer or mayinclude combinations of two or more different monomers within thatclass. The mole percent of each monomeric unit within a class ofmonomeric units may be independently selected.

a. Co-Crosslinking Monomeric Unit

The co-crosslinking monomeric unit of the temporary wet strengthadditives of the present invention comprises an electrophilic moiety andcan be derived from a monomer having the following structure:

wherein Y₁ and A are as defined above. If A is:

R₁ can be a substituted or unsubstituted, branched or linear aliphaticgroup. The aliphatic group preferably comprises a methylene or a C₂-C₁₈chain, more preferably a methylene or a C₂-C₇ chain, even morepreferably a methylene or a C₂ chain. Preferably, if R₁ is substituted,the substituent(s) will include an electron withdrawing functionality atthe alpha-methylene position relative to the aldehyde moiety. Suitableelectron withdrawing groups include, but are not limited to, halogens,such as chlorine, fluorine, and bromine; amides, such as —NHCOR′ whereineach R′ can independently be substituted or unsubstituted, branched orlinear C₁-C₁₂ aliphatic groups; hydroxyl groups; alkoxy groups,preferably with C₁-C₈ alkyl chains; cyano groups, e.g., —CN; and nitrogroups, e.g. —NO₂. The aldehyde functionality can optionally bechemically protected during polymerization by techniques well known inthe art.

Nonlimiting examples of suitable co-crosslinking monomeric units includeN-(2,2-dimethoxyethyl)-N-methyl acrylamide, acrolein, methacrolein,glyoxylated acrylamide, 3,3-dimethyoxypropyl acrylamide,3,3diethoxypropyl acrylamide, 3,3-dimethoxypropyl methacrylamide,2,2dimethoxy-1-methylethyl acrylate, 3,3-dimethoxypropyl methacrylate,2-(acryloylamino)ethanal dimethylacetal, 2-(methacryloylamino)propanaldimethyl acetal, 5-(acryloylamino)pentanal dimethylacetal,8-(acryloylamino)octanal dimethylacetal, and3-(N-acryloyl-N-methylamino)propanal dimethyl acetal.N-(2,2-dimethoxyethyl)-N-methyl acrylamide is most preferred. Othersuitable monomers are disclosed in U.S. Pat. No. 3,410,828, Kekishissued Nov. 12, 1986 and U.S. Pat. No. 3,317,370, Kekish, issued May 2,1967, both of which patents are incorporated herein by reference.

b. Homo-Crosslinking Monomeric Units

The homo-crosslinking monomeric unit of the temporary wet strengthadditives of the present invention comprises a nucleophilic moietycapable of forming an unstable, covalent bond with an electrophilicmoiety (i.e. aldehyde moiety present on a co-crosslinking monomericunit). As a result of this unstable covalent bond, the nucleophilicmoiety can crosslink together two or more temporary wet strengthadditives, at least one of which is a temporary wet strength additive ofthe present invention, via the unstable covalent bond formed between thenucleophilic moiety present on one temporary wet strength additive andthe electrophilic moiety present on another temporary wet strengthadditive. So in other words, a mixture comprising only temporary wetstrength additives of the present invention may be crosslinked togethervia the nucleophilic moiety, as described above, or a mixture oftemporary wet strength additives of the present invention with otherconventional temporary wet strength additives my be crosslinked togethervia the nucleophilic moiety present on the temporary wet strengthadditives of the present invention.

A nonlimiting example of a suitable nucleophilic moiety is ahydroxyl-containing moiety.

The homo-crosslinking monomeric unit of the temporary wet strengthadditives of the present invention, i.e. monomer units having Z attachedthereto in Formula I, can be derived from a monomer having the followingstructure:

wherein Y₃ and Z are as defined above. If Z is:

R₂ can be a substituted or unsubstituted, branched or linear aliphaticgroup. The aliphatic group preferably comprises a C₂-C₁₈ chain, morepreferably a C₂-C₇ chain, even more preferably a C₂-C₄ chain. If Z is—OH, the hydroxyl group in the homo-crosslinking monomer unit should bechemically protected during polymerization by techniques well known inthe art.

Nonlimiting examples of suitable homo-crosslinking monomeric unitsinclude the following: 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 4-hydroxybutyl acrylate, glyceryl mono-methacrylate,glyceryl mono-acrylate, 2-hydroxypropyl acrylate 2-hydroxypropylmethacrylate, hydroxypropyl acrylate 4-hydroxybutyl methacrylate,diethylene glycol mono-methacrylate, sorbitol methacrylate, methyl2-hydroxymethyl acrylate, 3-methyl butanol-2 methacrylate, 3,3-dimethylbutanol-2 methacrylate, ethyl 2-(hydroxymethyl)acrylate,N-2-hydroxyethyl methacrylamide, N-(2-hydroxypropyl)methacrylamide,2-acrylamidoglycolic acid, poly(ethylene glycol) acrylate andacrylamidotrishydroxymethylmethane.

Further nonlimiting examples of homo-crosslinking monomer units includepoly(ethylene glycol) acrylate having the formula:

wherein n is an integer from 2 to 100, preferably 2 to 50, morepreferably 2 to 30, and a homo-crosslinking monomer unit having theformula:

c. Cationic Monomeric Units

The cationic monomeric unit can be derived from any polymerizablemonomer which imparts a positive charge to the temporary wet strengthadditive of the present invention subsequent to polymerization. Cationicmonomer units may and preferably do carry a positive electrostaticcharge when dissolved in water. Suitable counterions can includechloride, fluoride, bromide, iodide, sulphate, methylsulfate, phosphateand the like.

Nonlimiting examples of suitable cationic monomeric units include3-(methacryloylamino)propyl trimethyl ammonium chloride,2-vinyl-N-methylpyridinium chloride, diallyldimethyl ammonium chloride,(p-vinylphenyl)trimethyl ammonium chloride, 2-(dimethylamino)ethylacrylate, 2-dimethylaminoethyl methacrylate,trimethyl(p-vinylbenzyl)ammonium chloride, p-dimethylaminoethylstyrene,dimethylaminopropyl acrylamide, 2-methylacrloyloxyethyltrimethylammonium methylsulfate, and 3-acrylamido-3-methylbutyl trimethylammonium chloride.

Further nonlimiting examples of the suitable cationic monomeric units ofthe present invention include:

d. Non-Nucleophilic and/or Nucleophilic Monomeric Units

The non-nucleophilic and/or nucleophilic monomeric unit (the monomericunit containing W) that does not form a stable covalent bond with theelectrophilic moiety (i.e., aldehyde moiety present on a co-crosslinkingmonomeric unit) can optionally be incorporated into the temporary wetstrength additive of the present invention.

The non-nucleophilic monomeric unit can be derived from a monomer havingthe following structure:

wherein W and Y₂ are as defined above, with Y₂ preferably being H.Preferably, W is hydrophilic. If W is a hydrophobic moiety, the amountincorporated (b) should be below levels that would result in a copolymerthat is insoluble in water.

Nonlimiting examples of suitable non-nucleophilic monomeric unitsinclude nitrogen heterocyclic moiety-containing monomeric units, such asvinyl oxazolidones, vinyl imidazoles, vinyl imidazolines, vinylpyridines, and vinyl pyrrolidones, such as N-vinyl pyrrolidone, 2-vinylpyrrolidone, etc.

Other specific nitrogen heterocycles useful as monomeric unit startingreagents include N-vinyl-5-methyl-2-oxazolidine, N-vinyl-2-oxazolidone,N-vinyl pyrrolidone, N-vinyl imidazole, N-vinyl-2-methyl imidazole,2-vinyl imidazole N-vinyl-3-morpholinone, N-vinyl caprolactam, etc.Preferred among these nitrogen heterocycles are the vinyl pyrrolidones.

Other nonlimiting examples of non-nucleophilic, hydrophilic monomericunits are N,N-dimethyl acrylamide and methoxy poly(ethylene glycol)methacrylate.

Nonlimiting examples of non-nucleophilc, hydrophobic monomeric unitsinclude alkyl, especially C₁-C₄, acrylate and methacrylate esters andstyrenes.

Nonlimiting examples of suitable non-nucleophilic monomeric unitsinclude methyl methacrylate, methyl acrylate, ethyl acrylate, n-propylacrylate, iso-propylacrylate, n-propyl methacrylate, ethyl methacrylate,iso-propylmethacrylate, n-butyl acrylate, isobutyl acrylate, isobutylmethacrylate, n-butyl methacrylate, α-methyl styrene, benzyl acrylateand ethylhexylacrylate.

In one embodiment, the non-nucleophilic, hydrophobic monomeric unitincludes a butyl acrylate.

Nonlimiting examples of nucleophilic monomeric units that do not formstable covalent bonds with the electrophilic moiety include carboxylicacids. Nonlimiting examples of suitable carboxylic acids include C₃₋₈monocarboxylic acids and C₄₋₈ dicarboxylic acids may be selected fromthe group consisting of acrylic acid, methacrylic acid,beta-acryloxypropionic acid, vinyl acetic acid, vinyl propionic acid,crotonic acid, ethacrylic acid, alpha-chloro acrylic acid, alpha-cyanoacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconicacid, citraconic acid, mesaconic acid, methylenemalonic acid, theirsalts, and mixtures thereof.

More preferably, the C₃₋₈ monocarboxylic acids, C₄₋₈ dicarboxylic acids,their salts and mixtures thereof, may be selected from the groupconsisting of acrylic acid, methacrylic acid, maleic acid.

It has been surprisingly found that fibrous structures and/or sanitarytissue products comprising a wet strength additive, especially atemporary wet strength additive, more especially a temporary wetstrength additive that comprises a non-nucleophilic monomeric unit, suchas butyl acrylate and/or a homo-crosslinking monomeric unit comprising apoly(ethylene glycol) acrylate moiety, for example, minimizes thenegative impact of creping on wet tensile of the fibrous structureand/or sanitary tissue product and/or improves the softness of thefibrous structure and/or sanitary tissue product as compared to afibrous structure and/or sanitary tissue product having a wet strengthadditive other than those described herein.

Without being bound by theory, it is believed that the wet strengthadditives of the present invention exhibit a lower Tg than conventionalwet strength additives and thus, as a result avoid fracturing during acreping process. By not fracturing during a creping process, loss of wettensile in a fibrous structure and/or sanitary tissue product comprisingsuch a wet strength additive, especially where the wet strength additiveexhibits a Tg of less than about 100° C., is mitigated or inhibited.

The temporary wet strength additives of the present invention can bemade by a wide variety of techniques, including bulk, solution,emulsion, or suspension polymerization. Polymerization methods andtechniques for polymerization are described generally in Encyclopedia ofPolymer Science and Technology, Interscience Publishers (New York), Vol.7, pp. 361-431 (1967), and Kirk-Othmer Encyclopedia of ChemicalTechnology, 3rd edition, Vol 18, pp. 740-744, John Wiley & Sons (NewYork), 1982, both incorporated by reference herein. See also Sorenson,W. P. and Campbell, T. W., Preparative Methods of Polymer Chemistry. 2ndedition, Interscience Publishers (New York), 1968, pp. 248-251,incorporated by reference herein, for general reaction techniquessuitable for the present invention. Preferably, the temporary wetstrength additives are made by free radical copolymerization, usingwater soluble initiators. Suitable free radical initiators include, butare not limited to, thermal initiators, redox couples, and photochemicalinitiators. Redox and photochemical initiators are preferred forpolymerization processes initiated at temperatures below about 30° C.(86° F.). Such initiators are described generally in Kirk-OthmerEncyclopedia of Chemical Technology, 3rd edition, John Wiley & Sons (NewYork), Vol. 13, pp. 355-373 (1981), incorporated by reference herein.Typical water soluble initiators that can provide radicals at 30° C. orbelow include redox couples, such as potassium persulfate/silvernitrate, and ascorbic acid/hydrogen peroxide. A preferred methodutilizes thermal initiators in polymerization processes conducted above40° C. (104° F.). Water soluble initiators that can provide radicals at40° C. (104° F.) or higher can be used. These include, but are notlimited to, hydrogen peroxide, ammonium persulfate, and2,2′-azobis(2-amidinopropane) dihydrochloride. In one especiallypreferred method, water soluble starting monomers are polymerized in anaqueous alcohol solvent at 60° C. (140° F.) using2,2′-azobis(2-amidinopropane) dihydrochloride as the initiator. Thesolvent should typically contain at least about 10% by volume, ofalcohol in order to prevent the polymerization reaction medium fromgelling. Suitable alcohols for use in such reaction include lowmolecular weight alcohols such as, but not limited to, methanol,ethanol, isopropanol, and butanol.

Another technique is a solution polymerization as described in U.S. Pat.No. 3,317,370, Kekish, issued May 2, 1967 and U.S. Pat. No. 3,410,828,Kekish, issued Nov. 12, 1968, both incorporated herein by reference.According to such process, the acrolein, or other aldehydic monomer, iscopolymerized with a non-nucleophilic, water soluble,nitrogen-heterocyclic polymerizable monomer and a redox initiatorsystem. The copolymer is then made cationic by reacting the copolymerwith a water soluble amine or amine quaternary. Amines, including aminequaternaries, that are useful include, but are not limited to, primary,secondary, and tertiary amines such as ethylene diamine, diethylenetriamine, triethylene tetramine, tetraethylene pentamine, or partial orfully quaternized derivatives of any of the foregoing, hydrazides andquaternaries thereof such as betaine hydrazide chloride,N—N-dimethylglycine hydrazide, unsymmetrical dimethyl hydrazides,polymers, such as those formed by reaction of urea and polyalkylenepolyamines, guanidines, biguamides, guanylureas, mono and polyhydroxypolyamines and quaternaries thereof, etc. When using this emulsioncopolymerization technique, it will be necessary to control molecularweight to within the ranges provided herein. Suitable methods for thisare discussed below.

Generally, as the weight average molecular weight of the temporary wetstrength additive is decreased, initial wet strength will become smallerand wet strength decay will become faster. The temporary wet strengthadditives of the present invention should have a molecular weight of atleast about 20,000, preferably at least about 70,000. The upper limitfor molecular weight will be limited by a combination of the ability ofthe additive to impart the desired level of strength decay, discussedfurther below, and practical considerations such as sufficiently lowviscosity for application to pulp slurries or pulp sheets and technicaland economic concerns related to formation of such high molecular weightadditives. Generally, the molecular weight should be less than about400,000, preferably less than about 300,000, and more preferably lessthan about 200,000.

Molecular weight can be controlled by such methods that are known tothose skilled in the art, such as varying reaction temperature(increased temperature typically results in reduced molecular weight),varying free radical initiator concentration, and utilization of chaintransfer agents. Suitable chain transfer agents include, but are notlimited to, beta.-mercaptoethanol, thioglycolic acid, glycerol, acetone,and isopropanol. Other suitable chain transfer agents include, but arenot limited to, those described in Polymer Handbook, 2nd edition, J.Brandrup and E. H. Immergut, editors, Wiley-Intersciences (New York),(1975), pp. 11-57 through 11-104, incorporated by reference herein.

NONLIMITING SYNTHESIS EXAMPLES Example I

Preparation of a Temporary Wet Strength Additive in Accordance with thePresent invention having the following structure:

N-(2,2-dimethoxyethyl)-N-methyl acrylamide (1.006 g, 5.807 mmole),2-hydroxyethyl acrylate (5.645 g, 48.58 mmole),[3-(methacryloylamino)propyl]trimethyl ammonium chloride (0.763 g, 3.46mmole), 2,2′-azobis(2-amidinopropane) dihydrochloride (0.0475 g, 0.175mmole), 2-propanol (5 ml), and water (45 ml) are added to a 250 ml roundbottom flask containing a magnetic stir bar. This solution is spargedwith Ar for 25 minutes and then the neck is fitted with a gas inletadapter connected to an Ar manifold. The flask is heated for 20 hours at60° C. in an oil bath. This polymer will have an acetal protectinggroup. A small analytical sample is reserved for gel permeationchromatography and proton NMR spectroscopy and then water (75 ml) and 1NHCl (14 ml) are added. The solution is heated at 40° C. for four hoursunder Ar to hydrolyze the protecting group. After cooling to roomtemperature, the solution is adjusted to pH 5 with 1 N NaOH and thendialyzed against water for 16 hours (Mw cut-off=3,500). The weightaverage molecular weight of this polymer will typically be about 140,000and a, c, and d will typically be between about 9% to about 11%, betweenabout 83% to about 85%, and between about 5% to about 7%, respectively.The Tg of this polymer will typically be about 77° C.

Example II

Preparation of a Temporary Wet Strength Additive in Accordance with thePresent invention having the following structure:

N-(2,2-dimethoxyethyl)-N-methyl acrylamide (61.54 g, 0.3553 mole),2-hydroxyethyl acrylate (330.01 g, 2.842 mole),[3-(methacryloylamino)propyl]trimethyl ammonium chloride (78.41 g,0.3552 mole), 2,2′-azobis(2-amidinopropane) dihydrochloride (2.891 g,10.7 mmole), 2-propanol (230 ml), and water (2.83 L) are added to a 12 Lthree-necked, round bottom flask fitted with a mechanical stirrer,temperature probe, and a gas inlet adapter. This solution is spargedwith Ar for 30 minutes and then heated from room temperature to 55° C.,with constant stirring under Ar, at which point the reaction becomesexothermic. The reaction temperature is maintained between about 58° C.to about 65° C. until the reaction is no longer exothermic. The solutionis heated at 60° C. for an additional 20 hours. This polymer will havean acetal protecting group. An analytical sample is reserved andcharacterized as described in Example I. The 2-propanol is removed invacuo and then the viscous solution is transferred to a 22 L threenecked, round bottom flask with water (5.74 L) and then concentrated HCl(77 ml) is added. The solution is heated at 40° C. for four hours undernitrogen to hydrolyze the protecting group. After cooling to roomtemperature, the solution is adjusted to pH 5 with NaOH. The weightaverage molecular weight of this polymer will typically be about 160,000and a, c, and d will typically be between about 7% to about 11%, betweenabout 80% to about 83%, and between about 9% to about 11%, respectively.The Tg of this polymer will typically be about 60° C.

Example III

Preparation of a Temporary Wet Strength Additive in Accordance with thePresent invention having the following structure:

N-Vinylpyrrolindinone (202.60 g, 1.823 mole), 2-hydroxyethyl acrylate(70.55 g, 0.6076 mole), [3-(methacryloylamino)propyl]trimethyl ammoniumchloride (67.07 g, 0.3038 mole), 2,2′-azobis(2-amidinopropane)dihydrochloride (8.23 g, 3.03 mmole), 2-propanol (525 ml), and water(2.1 L) are added to a 5 L three-necked, round bottom flask fitted witha mechanical stirrer, temperature probe, and a gas inlet adapter. Thissolution is sparged with Ar for 30 minutes and then acrylamide (21.59 g,0.3037 mole) is added. The solution is then heated from room temperatureto 58° C., with constant stirring under Ar, at which point the reactionbecomes exothermic. The reaction temperature is maintained between about58° C. to about 60° C. until the reaction is no longer exothermic. Thesolution is heated at 60° C. for an additional 20 hours. An analyticalsample is reserved and characterized as described in Example I. The2-propanol is removed in vacuo and then glyoxal (44.07 g of a 40%solution, 0.3037 mole) is added. The solution is maintained at pH 8 for8 hours by the addition of 10% NaOH and then allowed to stir overnightat room temperature. The solution is then adjusted to pH 5 by theaddition of 1N HCl. The weight average molecular weight of this polymerwill typically be about 150,000 and a, b, c, and d will typically bebetween about 8% to about 11%, between about 59% to about 61%, betweenabout 19% and 21%, and between about 9% to about 11%, respectively. TheTg of this polymer will typically be about 98° C.

Example IV

Preparation of a Temporary Wet Strength Additive in Accordance with thePresent invention having the following structure:

N-(2,2-dimethoxyethyl)-N-methyl acrylamide (45.71 g, 0.2369 mole),2-hydroxyethyl acrylate (214.55 g, 1.8477 mole),[3-(methacryloylamino)propyl]trimethyl ammonium chloride (58.27 g,0.2640 mole), n-butyl acrylate (33.83 g, 0.2682 mole)2,2′-azobis(2-amidinopropane) dihydrochloride (2.147 g, 7.917 mmole),2-propanol (152 ml), acetone (650 ml), and water (1.48 L) are added to a5 L three-necked, round bottom flask fitted with a mechanical stirrer,temperature probe, and reflux condenser. This solution is sparged withAr for 30 minutes and then heated from room temperature to 55° C., withconstant stirring under Ar, at which point the reaction becomesexothermic. The reaction temperature is maintained between about 58° C.to about 60° C. until the reaction is no longer exothermic. The solutionis heated at 60° C. for an additional 20 hours. This polymer will havean acetal protecting group. An analytical sample is reserved andcharacterized as described in Example I. The 2-propanol and acetone areremoved in vacuo and then the viscous solution is transferred to a 12 Lthree necked, round bottom flask with water (2.9 L) and thenconcentrated HCl (49 ml) is added. The solution is heated at 40° C. forfour hours under nitrogen to hydrolyze the protecting group. Aftercooling to room temperature, the solution is adjusted to pH 5 with NaOH.The weight average molecular weight of this polymer will typically beabout 92,000 and a, b, c, and d will typically be between about 9% toabout 11%, between about 9% and about 11%, between about 69% to about71%, and between about 9% to about 11%, respectively. The Tg of thispolymer will typically be about 75° C.

Example V

Preparation of a Temporary Wet Strength Additive in Accordance with thePresent invention having the following structure:

N-(2,2-dimethoxyethyl)-N-methyl acrylamide (0.997 g, 5.76 mmole),N-vinyl pyrrolidinone (1.925 g, 17.32 mmole), 2-hydroxyethyl acrylate(0.339 g, 2.92 mmole), [3-(methacryloylamino)propyl]trimethyl ammoniumchloride (0.639 g, 2.89 mmole), 2,2′-azobis(2-amidinopropane)dihydrochloride (0.0778 g, 0.287 mmole), 2-propanol (5 ml), and water(20 ml) are added to a 100 ml round bottom flask containing a magneticstir bar. This solution is sparged with Ar for 25 minutes and then theneck is fitted with a gas inlet adapter connected to an Ar manifold. Theflask is heated for 20 hours at 60° C. in an oil bath. This polymer willhave an acetal protecting group. An analytical sample is reserved andcharacterized as described in Example I and then the solution istransferred to a 250 ml round bottom flask with water (55 ml). 1N HCl(6.5 ml) is added and the solution is heated at 40° C. for four hoursunder Ar to hydrolyze the protecting group. After cooling to roomtemperature, the solution is adjusted to pH 5 with 1 N NaOH and thendialyzed against water for 16 hours (Mw cut-off=3,500). The weightaverage molecular weight of this polymer will typically be about 260,000and a, b, c, and d will typically be between about 18% to about 20%,between about 59% to about 61%, between about 9% to about 11%, andbetween about 9% to about 11%, respectively. The Tg of this polymer willtypically be about 177° C.

Example VI

Preparation of a Temporary Wet Strength Additive in Accordance with thePresent invention having the following structure:

N-(2,2-dimethoxyethyl)-N-methyl acrylamide (29.00 g, 0.1674 mole),2-hydroxyethyl acrylate (149.70 g, 1.289 mole),[3-(methacryloylamino)propyl]trimethyl ammonium chloride (36.96 g,0.1674 mole), poly(ethyleneglycol) acrylate (18.84 g, 0.0502 mole)2,2′-azobis(2-amidino-propane) dihydrochloride (1.37 g, 5.05 mmole),2-propanol (250 ml), and water (1.42 L) are added to a 5 L three neck,round bottom flask fitted with an overhead stirrer and a temperatureprobe, and the solution was sparged with Ar for 30 min. The third neckwas fitted with a gas inlet adapter connected to an Ar manifold. Thesolution was heated to 58° C. with a heating mantle. The reactiontemperature is maintained between about 58° C. to about 60° C. until thereaction is no longer exothermic. The solution is heated at 58° C. foran additional 20 hours. This polymer will have an acetal protectinggroup. An analytical sample is reserved and characterized as describedin Example I. The 2-propanol was removed in vacuo and then the viscoussolution is transferred to a 12 L three necked, round bottom flask withwater (1.74 L) and then concentrated HCl (30 ml) is added. The solutionis heated at 40° C. for four hours under nitrogen to hydrolyze theprotecting group. After cooling to room temperature, the solution isadjusted to pH 4 with NaOH. The weight average molecular weight of thispolymer will typically be about 121,000 and a, c1, c2, and d willtypically be between about 9% to about 11%, between about 2% and about4%, between about 76% to about 78%, and between about 9% to about 11%,respectively. The Tg of this polymer will typically be about 67° C.Test Methods% Decay Test Methoda. Sample Preparation—Handsheets

If a sample fibrous structure is not in existence, then a samplehandsheet can be prepared to test % Decay. Handsheets can be formed from100% unrefined Northern Softwood Kraft (NSK), mixtures of NSK andEucalyptus, or from other fibers as desired. After dispersing the NSK,or other fibers, in water, a temporary wet strength resin is added tothe disintegrated pulp and the slurry is agitated for a fixed period oftime ranging from 1 to 60 minutes. Handsheets are made essentiallyaccording to the TAPPI standard T205 with the following exceptions:

-   (1) the sheet is formed on a polyester wire and dewatered by suction    rather than pressing;-   (2) the embryonic web is transferred by vacuum to a polyester    papermaking fabric;-   (3) the sheet is then dried by steam on a rotary drum drier.    b. Testing

1. 11.33 cm (4.5 inch) wide by 10.16 cm (4 inch) long strips of fibrousstructure or sanitary tissue product to be tested are prepared. 2.54 cm(1 inch) wide sample strips are cut from the fibrous structure orsanitary tissue product.

2. In a conditioned room where the temperature 23±3° C. (73±4° F.) andrelative humidity 50±10% a sample strip [2.54 cm (1 inch) wide] ismounted onto an electronic tensile tester, an EJA Tensile Tester ModelNo. 1376-18 commercially available from Thwing Albert InstrumentCompany. The tensile tester is operated at a crosshead speed of 2.54cm/minute (1 inch/minute). The tensile device is fastened in the lowerclamp of the tensile tester such that the horizontal rod was parallel tothe clamp faces and is otherwise symmetrically located with respect tothe clamps. The position of the lower clamp is adjusted so that thehorizontal axis of the rod was exactly 1″ (2.54 cm) below the upperclamp.

3. A liquid container is filled to ⅛″ (0.3175 cm) from the top of thecontainer with standard tap water which contains 23 ppm calcium ion, 7ppm magnesium ion and 67 ppm sodium bicarbonate. The sample strip beingmeasured is threaded under the rod in the wet tensile device. The endsof the sample strip are placed together, the slack is removed and theupper clamp fastened. The sample strip is centrally located with respectto the horizontal rod and the upper clamp. The liquid container israised immersing the looped end of the sample strip to a depth of atleast ¾″ (1.9 cm). Exactly 5 seconds after the liquid container israised in place and with the liquid container remaining in place thetensile tester was engaged. The load is recorded. Wet tensile isexpressed in g/in (g/2.54 cm) units.

${{Average}\mspace{14mu}{Wet}\mspace{14mu}{Tensile}\mspace{14mu}\left( {g/{in}} \right)} = \frac{{sum}\mspace{14mu}{of}\mspace{14mu}{loads}\mspace{14mu}{at}\mspace{14mu}{peak}\mspace{14mu}{for}\mspace{14mu}{test}\mspace{14mu}{runs}}{{2 \times {number}}\mspace{14mu}{of}\mspace{14mu}{tensile}\mspace{14mu}{strips}\mspace{14mu}{tested}}$Wet Tensile is calculated for machine direction (MD) and cross-machinedirection (CD).Total Wet Tensile (TWT)=Avg. Wet Tensile (MD)+Avg. Wet Tensile (CD)

4. Next, a sample strip is clamped to the Intelect 500 as describedabove in Step 3. The liquid container is raised to its uppermostposition immersing the looped end of the specimen to a depth of at least¾″ (1.9 cm) in the standard tap water. 5 minutes after the liquidcontainer is raised in place the wet tensile load is again read.

${\%\mspace{14mu}{Decay}} = {\frac{\left( {{{TWT}\; 5\mspace{14mu}\sec\mspace{14mu}{soak}} - {{TWT}\; 5\mspace{14mu}\min\mspace{14mu}{soak}}} \right)}{{TWT}\; 5\mspace{14mu}\sec\mspace{14mu}{soak}} \times 100}$

5. Step 4 is repeated except that the sample strip is immersed in thestandard tap water for 30 minutes rather than 5 minutes. The % Decay iscalculated as follows:

${\%\mspace{14mu}{Decay}} = {\frac{\left( {{{TWT}\; 5\mspace{14mu}\sec\mspace{14mu}{soak}} - {{TWT}\; 30\mspace{14mu}\min\mspace{14mu}{soak}}} \right)}{{TWT}\; 5\mspace{14mu}\sec\mspace{14mu}{soak}} \times 100}$To illustrate nonlimiting embodiments of the present invention,handsheets containing the temporary wet strength resins of Examples I-Vand a prior art temporary wet strength additive, Parez® (BayerChemicals), were prepared as described herein and tested for initial wettensile and % Decay as described in the Decay Test Method. Results arepresented below:

Wet Tensile Decay Wet Strength Usage Rate Initial Wet (%) Additive(lbs./ton) Tensile (g/in) 5 min 30 min Parez ® 7 71 38 67 Example I 2107 60 84 Example II 4 98 60 78 Example III 2 80 63 81 Example IV 2 8367 85 Example V 2 71 44 68 Example VI 5 132 74 87

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be considered as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A temporary wet strength additive comprising an acrolein-free polymerbackbone comprising an internal homo-crosslinking monomeric unitcomprising a hydroxyl moiety and lacking electrophilic moieties andnucleophilic moieties that form stable, covalent bonds withelectrophilic moieties, a co-crosslinking monomeric unit and a cationicmonomeric unit, wherein the homo-crosslinking monomeric unit is derivedfrom a monomer having the following formula:

and X is —O—, —NH—, or —NCH₃—; and R₂ is independently selected from thegroup consisting of substituted or unsubstituted aliphatic groups; andY₃ is —H, —CH₃, or a halogen.
 2. The temporary wet strength additiveaccording to claim 1 wherein the temporary wet strength additive has thefollowing formula:

and X is —O—, —NH—, or —NCH₃—, and R₁ and R₂ are substituted orunsubstituted aliphatic groups; Y₁, Y₂, and Y₃ are independently —H,—CH₃, or a halogen; Q is a cationic monomeric unit; and W is anon-nucleophilic moiety or a nucleophilic moiety that does not form astable covalent bond with the electrophilic moiety, wherein the molepercent of a is from about 1% to about 47%, the mole percent of b isfrom about 0% to about 70%, the mole percent of c is from about 10% toabout 90%, and the mole percent of d is from about 1% to about 40%; andsaid temporary wet strength additive has a weight average molecularweight of at least about 70,000.
 3. The temporary wet strength additiveaccording to claim 2 wherein said weight average molecular weight isfrom about 70,000 to about 400,000.
 4. The temporary wet strengthadditive according to claim 2 wherein a is from about 5% to about 30%, bis from 0% to about 60%, c is from about 30% to about 80%, and d is fromabout 2% to about 20%.
 5. The temporary wet strength additive accordingto claim 2 wherein A is

and R₁ comprises a C₂-C₇ aliphatic chain.
 6. The temporary wet strengthadditive according to claim 2 wherein Z is

and R₂ is a C₂—C₄ aliphatic chain.
 7. The temporary wet strengthadditive according to claim 1 wherein the homo-crosslinking monomericunit is selected from the group consisting of 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutylmethacrylate, glyceryl mono-methacrylate, glyceryl mono-acrylate,2-hydroxypropyl acrylate 2-hydroxypropyl methacrylate, 3-hydroxypropylacrylate, 3-hydroxypropyl methacrylate, diethylene glycolmono-methacrylate, N-2-hydroxyethyl methacrylamide, N-(2-hydroxypropyl)methacrylamide, and acrylamidotrishydroxymethylmethane.
 8. The temporarywet strength additive according to claim 2 wherein the monomeric unitcomprising W is selected from the group consisting of vinylpyrrolidones, vinyl oxazolidones, vinyl imidazoles, vinyl imidazolines,N,N-dialkyl acrylamides, alkyl acrylates, and alkyl methacrylates. 9.The temporary wet strength additive according to claim 2 wherein themonomeric unit comprising W is a vinyl pyrrolidinone, and the monomericunit comprising Z is 2-hydroxyethyl acrylate.
 10. A fibrous structurecomprising a temporary wet strength additive according to claim
 1. 11.The fibrous structure according to claim 10 wherein the fibrousstructure comprises from about 0.005% to about 5% by weight of thefibrous structure of the temporary wet strength additive.
 12. Thefibrous structure according to claim 10 wherein the fibrous structureexhibits a % Total Wet Tensile Loss (Decay) after 5 minutes of soakingin neutral pH water of at least about 35% and/or a % Total Wet TensileLoss (Decay) after 30 minutes of soaking in neutral pH water of at leastabout 65% and/or an initial wet tensile strength/dry tensile strengthratio (WT_(i) /DT) of at least about
 7. 13. A single- or multi-plysanitary tissue product comprising a fibrous structure according toclaim
 10. 14. A surgical garment comprising a fibrous structureaccording to claim
 10. 15. A process for making a fibrous structurecomprising the steps of: a) providing a fiber furnish; b) depositing thefibrous furnish on a foraminous forming surface to form an embryonicfibrous web; c) drying the embryonic fibrous web such that the fibrousstructure is formed; and d) applying a temporary wet strength additiveaccording to claim
 1. 16. A process for making a sanitary tissue productcomprising the steps of: a) providing a fibrous structure in accordancewith claim 10; and b) converting the fibrous structure into a sanitarytissue product.
 17. A method for making a temporary wet strengthadditive comprising the steps of: a) providing a homo-crosslinkingmonomeric unit, a co-crosslinking monomeric unit and a cationicmonomeric unit, wherein the homo-crosslinking monomeric unit has thefollowing structure:

and X is —O—, —NH—, or —NCH₃—; and R₂ is a substituted or unsubstitutedaliphatic group; and Y₃ is —H, —CH₃, or a halogen; and b) polymerizingthe monomeric units from a) to form a temporary wet strength additiveaccording to claim 1.